QB Issue Resolution:

Since a SMLLC is treated as a Disregarded Entity, you will still be filing on a Sched C, so nothing really changed except you obtained an FEIN.

The reason you want new BANK and Credit Cards is so that the FEIN is on those accounts, now.

Resolution for Issue 'Should I have to create a NEW QB file going from Sole Proprietor to LLC of SAME company?' available: Yes (Solved).
Source: Intuit Community forum.

Should I have to create a NEW QB file going from Sole Proprietor to LLC of SAME company?: this issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the issue yourself by looking for a resolution described below. If it is a complex issue or you are unable to solve the issue, you may contact us by clicking here or by using other support options.

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